1. Field of the Invention
The disclosed and claimed concept relates to an adjustable frequency drive and, more particularly, to a hybrid heat management system for an adjustable frequency drive.
2. Background Information
Adjustable frequency drives are commonly used to drive AC induction motors allowing for its speed control. Adjustable frequency drives generally provide the advantage of energy savings because they control the characteristics of its output voltage and current, and thus controlling the motor speed (of the motor they are driving) by the user, optimizing the motor power usage as well as the process it is driving. Adjustable frequency drives operate by taking either incoming AC or DC power, having a fixed frequency and voltage, and converting it to AC power having a voltage or current with variable amplitude and frequency. This allows for the control of the motor speed and power, a requirement in many applications.
An adjustable frequency drive includes a number of power modules. Each power module includes a number of inverters and a transformer. The inverters and a transformer are electrically coupled through electrical buses and physically coupled through their respective bases. Each inverter includes a number of power poles. Each power pole includes, among other elements, a number of power semiconductor switches, a power supply and a gate driver, thermally coupled thereto, a plurality of capacitors, a plurality of electrical buses connecting the power semiconductor switches to the capacitors, and an insulative medium which encases or covers some or all of the electrically live components, such as the electrical buses.
An adjustable frequency drive generates heat and is, generally, disposed in enclosed housing. To dissipate the heat, the adjustable frequency drive includes a cooling system. Due to the amount of heat generated, adjustable frequency drives use a circulating liquid. That is, heat management assemblies such as, but not limited to, a forced air assembly or a heat sink, do not provide sufficient heat transfer so as to maintain the adjustable frequency drive at an operating temperature.
The power poles may share a common cooling system. That is, an AC drive is made up of a plurality of inverter modules, which are connected to a converter module to create the AC drive, wherein each of the above components is mounted on a cold plate coupled to a heat exchanger or liquid cooling system. Generally, the power poles are coupled directly to the cold plate and a number of power semiconductor switches, also identified as “cells,” are in fluid communication with the cold plate.
That is, the liquid cooling system for an inverter includes a primary cold plate, a number of cell cold plates, a forced air heat exchanger, and a plurality of conduits. The “primary cold plate,” as used herein, is a plate sized to accommodate a number of inverters being coupled directly thereto. A “cell cold plate” is a smaller element sized to accommodate a semiconductor switch, see e.g., U.S. Pat. No. 6,166,937. The conduits include transfer conduits, internal conduits, and cell conduits. The transfer conduits include a supply conduit and a return conduit. The transfer conduits are coupled to, and in fluid communication with, the forced air heat exchanger. The internal conduits are passages within a generally planar cold plate. The passages are, in one embodiment, labyrinthine. The cold plate includes a cool liquid supply port (inlet), a warm liquid port (outlet), and a number of cell ports, including both inlet and outlet ports. The cell conduits are coupled to, and in fluid communication with, the cell ports.
Thus, the liquid cooling system operated as follows. Cool fluid, i.e. a liquid coolant, is transferred from the heat exchanger via the supply conduit to the primary cold plate. Within the primary cold plate, the fluid absorbed heat from the inverter. A portion of the cool fluid, now somewhat heated, was further passed to the number of cell cold plates via the cell conduits. The fluid would absorb further heat from the individual cell cold plates before returning to the primary cold plate. The now warm fluid exited the primary cold plate and was transferred to the heat exchanger via the return conduit. The fluid was then cooled in the heat exchanger and cycled through the liquid cooling system again. With regard to the cell cold plates, there are a plurality of cells for each inverter; in one embodiment, there are eighty-eight cells. In this configuration, there are 176 cell conduits either providing cool liquid to, or removing warm liquid from, various cells.
Further, the forced air heat exchanger is located at a location separated from the inverter. That is, the forced air heat exchanger was spaced from the inverter housing assembly enclosure, and/or, disposed in a generally enclosed housing that was separate from the inverter housing assembly enclosure. Thus, moving air did not pass over the inverter. Thus, one reason each cell needed to be coupled to the liquid cooling system was that the liquid cooling system was to only cool the system within the inverter housing assembly enclosure.
Each conduit and port has the potential to leak. This is a disadvantage as the conduits tend to be disposed adjacent to the electrical components. Further, when a power pole needed to be removed, each conduit had to be decoupled from the primary cold plate. Thus, in the exemplary power pole discussed above, 176 conduits needed to be decoupled. This is a disadvantage because the removal of the power poles was labor intensive and because each decoupled conduit provided a potential for contaminating the cooling fluid.
There is, therefore, a need for a primary cold plate including a limited number of fluid ports. There is a further need for an inverter wherein the power poles are cooled by more than a single cooling system.